This invention relates to the prevention of a plan disease by specific inhibition of fungal polyamine biosynthesis.
Fungi attack a wide variety of economically important crop plants, substantially reducing their quality and yield. The major weapon used against such phytopathogens has been synthetic fungicides. We report here on the fungicidal and plant protective efficacy of DL-alpha-difluorimethylornithine (DFMO), a specific inhibitor of ornithine decarboxylase (ODC; EC 4.1.1.17), the enzyme that provides fungi with the polyamines needed for normal growth and development (Tabor, C. W. & Tabor, H (1985) Microbiol. Rev. vol. 49, 81-99). The differential toxicity of DFMO for fungi and higher green plants depends on the fact that the latter have an alternative pathway, based on arginine decarboxylase (ADCl EC 4.1.1.19), for the synthesis of essential polyamines. In previous in vitro, experiments with fungi grown on synthetic media (Rajam, M. V. & Galston, A. W. (1985) Plant Cell Physiol. vol. 26, 683-692), we showed that DFMO is an effective inhibitor of mycelial growth and that such inhibitions are readily reversed by applied putrescine or spermidine. For the important rust and mildew diseases, however, the obligately and biotrophically parasitic organisms cannot always be grown on synthetic media. We accordingly undertook experiments which show that DFMO can inhibit germination, growth, and pathogenic effects of those fungi as well as non-obligate fungi, inoculated onto leaves of susceptible plants. In vitro experiments alone are inadequate to establish the efficacy of DFMO control of pathogenic fungi on plant hosts.